Please note the paragraph:
All leading computer models of the global climate system indicate that
natural variability isn't enough to explain the changes being observed,
causing most observers to conclude that human activities, notably the
emission of carbon and other heat-trapping greenhouse gases, are the
culprit.




Global warming study forecasts more water shortages
Climate change already affecting Sierra snowpack
Carl T. Hall, Chronicle Science Writer

Thursday, November 17, 2005






A warmer world is virtually certain to be much thirstier, too,
according to a new study by West Coast researchers of the impact of
global warming on water supplies.

Climate change experts led by Tim Barnett at the Scripps Institution of
Oceanography in La Jolla (San Diego County) found that at least
one-sixth of the world's population, including much of the industrial
world and a quarter of global economic output, appeared vulnerable to
water shortages brought about by climate change.

Details appear today in the journal Nature, along with a separate study
suggesting climate models are proving to be an effective way of
analyzing and forecasting disruptions in water supplies brought on by
global warming.

Most experts see a clear warming trend over much of the world, although
regional impacts may vary. All leading computer models of the global
climate system indicate that natural variability isn't enough to
explain the changes being observed, causing most observers to conclude
that human activities, notably the emission of carbon and other
heat-trapping greenhouse gases, are the culprit.

Earlier work by Barnett and others has documented the regional impact
of climate change on California, much of which depends on seasonal
snowmelt in the Sierra Nevada to keep water taps flowing and farmlands
irrigated.

The latest study was an attempt to expand this sort of regional study
to encompass the entire globe, by identifying areas most likely to feel
the pinch of declining water supplies because of their reliance on
glacial mel****er and snowmelt.

Barnett and his colleagues -- Jennifer Adam and Dennis Lettenmaier of
the University of Washington -- excluded some areas, including
watersheds of the Colorado River in the western United States and the
Angara River in Asia, where reservoir storage capacity was judged large
enough to "buffer large seasonal stream flow shifts."

Some heavily populated areas downstream of clearly runoff-dependent
regions also were excluded -- even though they, too, would most likely
suffer -- simply because the scientists lacked a reliable data source.

Despite this conservative approach, Barnett said in an interview, he
was a bit taken aback by the extent of the world map falling within the
climatic red zone of impending water difficulties.

"This shows a rather dramatic region, a surprisingly large part of the
Earth, where you would expect to have serious water-supply problems in
the next several decades," Barnett said.

The warming trend already is showing effects in California's Sierra
Nevada snowpack, this region's main water source.

Climate models suggest average temperatures in the West will be about 1
to 3 degrees warmer by 2050 than at present. Even though total
precipitation isn't expected to change by much, because of the higher
temperatures more of it will come as rain rather than snow. At the same
time, the spring runoff will come about one month earlier in the year.

Expanding populations, agricultural and industrial interests, and the
need to keep streams flowing to protect vulnerable fish and other
species all promise to make the water situation even worse as the
climate shifts.

"I think this will be one of the first greenhouse gas-related problems
that will fall on the civilized world," Barnett said.

Some parts of the world, including a broad swath of Asia and India,
rely heavily on glacial runoff during summer months. That flow is
expected to increase as the glaciers recede because of warming, but
that just means the "water shortage, when it comes, will likely arrive
much more abruptly, in time, with water systems going from plenty to
want in perhaps a few decades or less," Barnett said.

All long-term climate projections are subject to attack from skeptics
who either doubt the reliability of the computer models or caution
against overreacting. The Bush administration and allied climate
advisers have adopted a generally cautious approach, calling for more
study of the problem.

Bonner Cohen, a senior fellow at the conservative National Center for
Public Policy Research in Washington, D.C., said it would be only
prudent for water planners in the zone Barnett identified to expand
their storage capacity -- just in case.

"The one word of skepticism I have on these studies is that ultimately
we are talking about modeling, and modeling just doesn't have a good
track record for predicting the future," he said. "Basing public policy
just on climate models can be a very, very risky business. I would be
very dubious selecting one study, no matter how well peer-reviewed,
predicting the climate 25, 50 or 100 years into the future, when there
are so many factors involved in the climate that at this point are so
poorly understood."

A separate study in Nature, by P.C.D. "Chris" Miller of the U.S.
Geological Survey and colleagues, added some reassurances on that
score, suggesting that "an ensemble" of 12 computer climate models all
pointed in essentially the same troubling direction: less available
water for a warming planet.